This invention is related to primary electrochemical cells. More particularly, it is concerned with extremely thin hermetically sealed batteries.
Primary electrochemical cells are employed for a wide variety of applications and are commonly available in a variety of sizes and shapes. For certain applications it is required that a cell supply low currents over an extended period of time. Under these conditions it is frequently desirable that the cell be hermetically sealed to preclude the possibility of the contents escaping into the surrounding environment. In addition, for use in applications such as electronic watches a cell must be of very small size and of thin configuration.
Primary cells employing electrochemical systems utilizing alkali metal anodes, such as lithium, carbon cathodes, and electrolytes of a solute dissolved in an inorganic oxyhalide or thiohalide solvent have high discharge capacity and are of small size. One example of a battery of this general type is shown in U.S. Pat. No. 4,121,020 entitled "Ultra-Thin Button-Type Primary Electrochemical Cell" which issued to James Epstein and William P. Brissette on Oct. 17, 1978 and is assigned to the assignee of the present application. Another primary electrochemical cell employing the same electrochemical system is shown and described in application Ser. No. 870,429 filed Jan. 18, 1978 by James Epstein and Nikola Marincic entitled "Hermetically Sealed Button-Type Electrochemical Cell and Method for Making Same" and also assigned to the assignee of the present invention.
For certain types of applications, however, for example, electronic watches employing liquid crystal displays (LCD), a voltage of at least 6 volts is required to operate the liquid crystal display. In watches utilizing conventional types of power supplies a 1.5 volt silver-zinc cell is usually employed together with electronic circuitry to step up the voltage to the necessary level to operate the display. Electrochemical cells such as the lithium-carbon type described in the aforementioned patent and application have an output of 3.6 volts and thus do not provide the desired voltage levels.